Defect monitoring and control are critically important in the manufacturing and production of large substrates like for example the substrates used in flat panel displays (FPDs). The FPDs are flat panel display screens used for portable personal computers (PCs), flat desktop monitors, mobile phones and digital devices, car navigation systems, video cameras, projection and the recently introduced flat and thin LCD televisions, and many other large and small display screens on various devices and appliances. The FPDs include, for example, Thin Film Transistor-Liquid Crystal Display (TFT-LCD) substrates. A typical LCD consists of two transparent substrates (typically glass) with control circuitry (TFT) and optical filters printed on their surfaces and filled with liquid crystal material between the two substrates. The FPD manufacturing process is complex and carried out in a highly sterile environment. Production of FPDs is susceptible to various defects introduced during the fabrication process, which may force the manufacturer to discard or repair panels. Hence the production yield suffers and product cost increases. Therefore, detection of defects in the substrates is critical to the manufacturer's success.
There are many types of defects in the TFT manufacturing process, including, but not limited to, fall-ons (particles of foreign material that fell on the glass during manufacturing), opens and shorts (a trace that became open and separate traces that became connected, respectively), chemical residues (puddles of chemicals left on the surface), and pinholes (through holes that create shorts between layers). These defects can result in deficiencies from dead pixels to malfunctioning panels.
Substrate inspection during steps of the manufacturing process facilitates quality control and process control, and helps minimize material loss resulting from those manufacturing defects. The inspection of FPDs presents special technological challenges because of the transparent materials used, multi-layer structure, high-density features, fine nature of potential defects (measured in single microns), large substrate area, and tact time (i.e., throughput) requirements. Automatic optical inspection (AOI) is used in the manufacturing processes of TFT-LCDs and semiconductor integrated circuit (IC) chips to diagnose the quality of manufactured components and improve the yield of the production, thus reducing manufacturing costs.
Conventional AOI systems use a camera to generate an image of the substrate. The resulting image is analyzed in an attempt to detect defects in the substrate. Analysis of the image provides information of defects, where the defect information includes one or more of location (e.g., x-coordinate position, y-coordinate position, data, gate, zone, etc.), size, and type of the defect. Additionally, the analysis provides information of trends in the number of defects as well as the defect type and location. The information of the analysis helps manufacturers optimize their yield management.
The fundamental performance of AOI is measured predominantly using the key specifications of speed and sensitivity of inspection. The advances in manufacturing technology have lead to higher speeds of fabrication, substrates having increasingly larger sizes, and printed patterns (on substrates) having ever smaller dimensions, all of which result in a more demanding need for AOI with higher speed and better sensitivity. Consequently, there is a need for AOI systems and methods that provide relatively high-speed analysis of large panel substrates (e.g., LCD glass substrates, semiconductor wafers, etc.) while delivering high resolution images and providing higher levels of sensitivity in defect detection.